Add ubuntu-24.04-arm to build-codeql matrix

[mbg]

What are you trying to accomplish?

CodeQL has recently started supporting arm64-based Linux platforms. The Dependabot proxy is used by the github/codeql-action/start-proxy action, but we don't currently generate suitable binaries here. As a result, Code Scanning Default Setup workflows that otherwise now support arm64-based Linux runners choke on the github/codeql-action/start-proxy step. This PR adds ubuntu-24.04-arm to the build matrix for the build-codeql job in the ci.yml workflow to produce suitable binaries for that platform.

Anything you want to highlight for special attention from reviewers?

This extends this setup that was previously added in a PR on the internal repository before it was open-sourced.

Now that this repository is open-source, it would be nice if we had proper releases of the proxy.

How will you know you've accomplished your goal?

Once the workflow successfully produces compatible binaries, I will test these separately with a modified github/codeql-action/start-proxy in a test repository.

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[mbg]

The artifact produced by the workflow running for this PR produces the expected binary type:

ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically linked, Go BuildID=...

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused workflow change correctly builds and uniquely names the ARM64 artifact.

Review effort: Balanced
Findings: None

What changed in this PR

Adds an ARM64 Linux binary for CodeQL’s proxy integration.

Changes:

• Adds ubuntu-24.04-arm to the build matrix.
• Names its artifact dependabot-proxy-linux-arm64.

File	Description
.github/​workflows/​ci.yml	Builds and uploads the ARM64 Linux proxy artifact.

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[jeffwidman]

Works for me!

As far as regularly releases of the proxy, I suspect non one on the Dependabot team at GitHub would mind you cutting releases, but for our workflows probably not something that really matters to us.

But we should probably take that discussion internally so feel free to raise it as a topic on the Github internal slack #dependabot channel.

[jeffwidman]

ubunut-latest is shifting to 26.04 in late Oct-November timeframe.

@mbg can you own circling back at that point to bump this up then?

[jeffwidman]

I'd be also very okay with simply starting with this on ubuntu-26.04-arm as of right now from the jump.

That way we don't have to circle back and it wont be out of sync for more than a month...